This invention relates to a selectively engageable and disengageable coupling having a rotatable member, a coiled helical spring and an intermittently rotatable control collar operable to expand and contract the spring relative to the rotatable member to change the state of engagement of the coupling.
More specificaly, the invention pertains to a coupling in the form of a clutch in which the spring normally is contructed around coaxial input and output members to couple the members for rotation in unison and in which the control collar is telescoped over the members and is anchored to one end of the spring. The collar normally rotates in unison with the members but is operable when stopped by an interposer to cause unwinding of the spring and thereby effect disengagement of the clutch. When the clutch is disengaged, the input member continues to rotate while the output member stops in an angular position determined by the angular position of the interposer.
A clutch of this general type is disclosed in Baer et al U.S. Pat. No. 3,726,372. In the Baer et al clutch, the interposer engages a single stop on the control collar and thus the output member is stopped in the same angular position each time the interposer is acutated to its active position and engages the stop. Because the control collar has only a single stop, the output member must turn through one or more full revolutions before the clutch can be disengaged.
Helander U.S. Pat. No. 3,835,972 discloses a helical spring clutch in which the control collar may be formed with more than one stop for engaging the interpose. With this arrangement, the clutch may be disengaged to effect indexing of the output member to a plurality of angularly spaced positions corresponding to the number and angular spacing of the stops.
In certain instances, it is desirable to stop the output member in a plurality of angular positions which may be selectively changed. To this end, the Helander control collar may be selectively rotated on the output member to adjust the angular position of the stops relative to the output member and the interposer. This enables the output member to be stopped in different angular positions relative to the interposer but does not permit changing of the angular spacing between the positions.
An arrangement in which the angular spacing between the stopped positions of the output member can be changed is disclosed in Schulman U.S. Pat. No. 3,979,975. In this arrangement, use is made of a plurality of angularly spaced interposers whose angular spacing can be selectively adjusted. The interposers are adapted to sequentially engage a stop on the control collar and thus the angular spacing between the stopped positions of the output member can be changed by adjusting the angular spacing of the interposers.